Particles - Objects Order
Use these arrows to reorder them to your liking. They will spawn in that order (if pick random is not checked ofc):



If you need to do this on hundreds of objects do it witch python:

import bpy

# change the active item to be moved (the blue highlighted row in upper image)
bpy.data.particles["ParticleSettings"].active_dupliweight_index = 1

# move it up or down:
bpy.ops.particle.dupliob_move_up()
bpy.ops.particle.dupliob_move_down()